The invention relates to the assembly of flexible substrates, for instance strips of substrates which are unwound from respective supply rolls and mutually connected by means of glue, to form a laminate by a laminating process.
The invention relates particularly to a laminating process wherein at least one of the substrates comprises a foam layer. A laminate manufactured on the basis thereof is for instance used in the car industry for covering seats or the like.
Known is a method which is known as xe2x80x9cflame laminationxe2x80x9d, wherein isocyanate, halogens, phosphorus-based compounds and the like are released. It is an object of the invention to provide a laminating device is which does not have this drawback and is therefore considerably more environmentally-friendly.
It is further known to perform a laminating process with a substrate provided with a foam layer or consisting of a foam layer, wherein as a result of the rather low temperature at which the two substrates are pressed toward each other in the pinch between two pressure rollers the foam layer loses a considerable part of its thickness. Since the thickness is of great importance in the case of the laminates in question, this loss of thickness is perceived as a great drawback, since in practice an excess of foam is used with such a method to obtain laminate which, despite the loss of thickness, still possesses the finally desired thickness. Said excess means the use of more material and higher costs.
In respect of the above the device provides a laminating device, comprising:
two pressure rollers pressed toward each other and together defining a pinch;
first feed means for guiding to the pinch a strip of a flexible first substrate provided with a thermally-activated glue layer, which first feed means comprise first heating means for heating the first substrate with the glue layer;
second feed means for guiding a flexible second substrate to the pinch such that this second substrate and the glue layer are pressed against each other by the pressure rollers; and
second heating means placed in the zone of the pinch upstream thereof for heating the first substrate with the glue layer heated by the first heating means and the second substrate immediately prior to the joining together thereof in the pinch, such that a laminate is formed consisting of two substrates mutually connected by the glue layer.
A steady and very effective preheating of the first substrate together with the glue layer is obtained by making use of a relatively long residence time in the region of the first heating means. It must nevertheless be prevented that these heating means take up too much space. A very practical embodiment has the special feature in this respect that the first heating means comprise a heated roller, around a substantial peripheral part of the outer surface of which the first substrate extends during transport at a relative speed of zero or practically zero. The roller can for instance be heated by thermal oil.
A specific embodiment has the special feature that the glue layer lies directly against the outer surface of the roller. It should be understood in this respect that the glue layer must be thermally activated. This can best take place by means of direct contact with the heat source, in this case the heated roller.
In order to prevent unintended adhesion of the glue layer to the roller use is preferably made of an embodiment in which the outer surface is coated with an anti-adhesion layer, for instance a coating not allowing adhesion to the glue layer, for instance a silicone material, PTFE or the like.
A greatly improved intensity of the activity of the first heating means is realized with an endless belt under tensile stress which extends over at least a part of said peripheral part of the outer surface and presses the first substrate with the glue layer against this outer surface.
In order to prevent problems with adhesion, for instance in the case where the first substrate is relatively porous and the glue softened by heating can penetrate to the other side of the first substrate, use can preferably be made of an embodiment in which the inner surface of the endless belt is coated with an anti-adhesion layer, for instance of silicone material, PTFE or the like.
So as to improve the intensity with which the glue is adhered to the first substrate, use can be made in a preferred embodiment of a third pressure roller which forms a second pinch with the heated roller and which at the end of the contact zone of the first substrate with the glue layer against the heated roller brings the heated and thereby softened glue into intensive contact with the first substrate, such that the glue can penetrate into pores possibly present in this first substrate.
A specific embodiment has the special feature that the second heating means are adapted and disposed to heat by infrared radiation at least the glue layer and the side of the second substrate for placing into contact therewith. Infrared radiation is generally very practical and can herein be dosed extremely well, for instance by adjusting the current flow through an incandescent element and/or adapting the distance of the infrared source relative to the receiving object.
A preferred embodiment has the special feature that the second heating means comprise only one infrared radiator.
Another embodiment has the special feature that the second heating means are adapted and disposed to heat by hot air at least the glue layer and the side of the second substrate for placing into contact therewith. This embodiment has the advantage that the risk of for instance any fire hazard or other disturbances in the case of unintentional standstill of the device is smaller than when infrared technique is used.
A preferred embodiment has the special feature that the residence time of the second substrate in the region of the second heating means and the energy density are chosen such that the second substrate is heated to a temperature of about 140xc2x0 C. Thus is achieved that the two layers for placing into mutual contact have roughly the same temperature in the region of the pinch. This enhances a rapid and completely reliable adhesion.
A specific embodiment of the latter principle has the special feature that the residence time of the second substrate in the region of the second heating means amounts to about 0.5-2 s and the energy density amounts to about 7-25 kW/m2.
As is known, efforts are increasingly being made to make materials reusable or embody them such that they can be easily separated from other materials for specifically adapted destruction. In this respect the laminator according to the invention can be embodied such that the substrates and the glue layer are based on materials chosen such that the laminate has substantially the character of a mono-material.
Applying of the glue to the first substrate can take place in different ways. The substrate can be already provided beforehand with a thermoplastic glue layer, although the laminator according to the invention can also be provided with means for applying such a glue layer. Mentioned by way of example are solvent-free spraying, applying a coating via an extrusion gap, powder-spraying and screen-coating.
Depending on the nature of the laminate for manufacture, a density of for instance 1-150 g/m2 can be used.
The processing speed of the laminator according to the invention depends on the technical requirements of a user. Speeds up to about 100 m/min. are easy to realize.
In respect of the width of the substrates and the final laminate, values in the order of a few meters, for instance 6 meters, can for instance be envisaged.